Fall 2005 Internet2 Member Meeting

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Debugging Path MTU Discovery Failures - Techniques and Results

Time 09/21/05 04:30PM-05:30PM

Session Abstract

The Internet Protocol supports the use of varying packet sizes, using a set of ICMP messages and a mechanism known as Path MTU Discovery (PMTUD). Although the most common maximum packet size is 1500 bytes, the use of larger, or jumbo packets is of particular interest to high-bandwidth applications and is supported in many R&E networks. PMTUD is critical to the use of jumbo packets in any practical network. However, there is a widespread perception that PMTUD is not working well in the modern Internet, and that enabling jumbo packets will add to the problem. In this talk, we describe algorithms for determining that PMTUD has failed on a path, and for finding the location and nature of the failure. We also present empirical results of using a PMTUD diagnostic tool in a variety of scenarios. We show that although the common practice of blocking ICMP messages is a problem, there exist other failure modes for both 1500-byte and jumbo paths.


Speaker William Owens NYSERNet

Presentation Media

Secondary tracks Network Planning and Engineering Advanced Applications and Technologies

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